Arc detection is an enhancement to thermal magnetic overload detection typically used in circuit breakers, which otherwise may not detect and respond to arc faults. A number of devices for detecting arc faults and methods of detection have been used in the past. These include the use of electrical (E) and magnetic (B) field arc sensors, detecting the amplitude of the rate of change of current signals when an arc fault occurs, the use of non-overlapping band pass filters to detect white noise that is characteristic of arcs, and detecting the disappearance of signals indicating the presence of arcs near zero current crossings. While some of these techniques are more or less effective, they require relatively sophisticated arc sensors and circuits and heretofore, most of these arc detection circuits have been incorporated in circuit breakers.
A number of devices and methods for detecting ground faults have been used in the past. Typically, ground faults are detected using B field sensors for sensing a difference between line neutral current together with integrators or low pass filters and are more or less effective. Heretofore, ground fault detection circuits have been incorporated in circuit breakers or receptacles.
U.S. Pat. No. 5,729,145 (Frederick K. Blades), the entire disclosure of which is incorporated herein by reference, discloses where an arcing in an AC power system is detected by monitoring the power waveform for wideband high-frequency noise, and examining the detected noise for patterns of variation in its amplitude synchronized to the power waveform. A narrowband, swept-frequency detector and synchronous averaging may be employed to improve discrimination of arc noise from background interference. An arcing fault interrupter for controlling a single circuit, and a whole house monitor, for detecting arcing anywhere in a house, are described. Also disclosed is an arc fault detection system with visual indicators. The device circuit includes a microprocessor that illuminates the green status light under normal conditions. The invention also discloses a method to relay a reported “health” of the electrical system by using different colors. In case of possible hazardous arcing, the microprocessor turns off the green light and illuminates the yellow light. This light remains illuminated until reset by the user that is done by depressing the reset button. In case when the arcing is deemed demonstrably hazardous, the microprocessor turns off the yellow light, and turns on the red light, indicating that a serious hazard exists. When this happens, microprocessor also periodically beeps the audible enunciator to call attention to the load center and inform the residents of the hazard. This detector must be manually reset by depressing the reset switch to clear the alarm status and reset the green light.
U.S. Pat. No. 6,421,214 (Thomas N. Packard, et al.), the entire disclosure of which is incorporated herein by reference, discloses a self-testing arc fault or ground fault detector includes arc fault detecting circuitry and components. The detector includes a testing circuit that tests at least part of the circuitry and components and generates a recurring signal when the test completes successfully. If the test does not complete successfully, the signal is lost. This loss of signal is signaled by an indicator connected to the testing circuit. In one version, the loss of signal activates a circuit interrupter that disconnects the load side of the detector from the line side. The use of a combination of lights to illuminate and indicate malfunction and/or faults is also disclosed.
U.S. Pat. No. 6,426,634 (Robert Henry Clunn, et al.), the entire disclosure of which is incorporated herein by reference, discloses a circuit switching device or circuit breaker with integrated self-test enhancements. The circuit breaker has separable contacts operable under processor control to control power to a circuit responsive to at least one of a plurality of fault conditions. The circuit breaker is operable according to a method for testing, the method includes the step of: controlling the switching device during a sampling cycle, to input one or more operating parameters sensed in the circuit to an A/D converter for measurement. The operating parameters enable detection of the fault conditions. The method continues by determining whether to read a select one of the operating parameters from an output of the A/D converter into a first memory. The pre-determined parameter values are read from a second memory into the first memory during the sampling cycle. The pre-determined parameter values are read instead of the operating parameters read from the A/D converter if a self-test has been invoked during the sampling cycle. Also, disclosed is that during the self-diagnostic tests for an arc fault protection device, if failures occur, the trip and/or fault code corresponding to the fault can be stored in the memory of a central processing unit (CPU). This code can be recovered by service personnel for further examination using RS-232 communications port.
It should be appreciated that the “visual indicators” of the prior art do not have the ability to remember what happened once the circuit breaker has been reset. If the user or homeowner locates or determines the presence of an electronic trip, the visual indicators may show whether the trip conditions was electronically generated, such as, GFCI or AFCI related, and upon resetting the circuit breaker, and if the condition does not repeat, the information is lost.
Similarly, the prior art visual indicators only display whether the fault was generated due to an arc/ground fault or an over-current fault. However, there is no way of telling specifically if the fault was an arc fault or a ground fault.
Furthermore, the prior art multiple visual indicators, which are in the form of different colors while the device is in operation require periodic monitoring by the user or operator to understand the effect of the color change, thereby, creating a burden for the user or operator to regularly open the load center.
Additionally, display of indicators in different frequencies to depict malfunction and/or faults is dependent on the correct interpretation of the human vision. There is a strong emphasis on the ability to detect and differentiate the separate flashing rates. This might cause erroneous judgment and result in false diagnosis.
The audible indicators of the prior art also do not result in a safe shutting off the device. Though they bring the arc fault detection to the user's notice, they do not function as intended by shutting off the current supply when an arc is detected. This becomes more apparent if the user is not physically present at the location when the arc fault is detected. In other words, manual intervention is necessary to fully check the device as well as recognize the correct operation and status. If the user is not present, the device might continue to produce the audible alarm instead of disarming and preventing further damage.
Therefore, there is a need for improvement in a fault circuit interrupter (FCI), and in particular in a visual indication of fault status, storage and clearance in an arc fault circuit interrupter (AFCI) and/or a ground fault circuit interrupter (GFCI).
This invention improves on the deficiencies of the prior art and provides an inventive visual indication of fault status, storage and clearance in an Arc Fault Circuit Interrupter (AFCI).